Quantum engineering of spin and anisotropy in magnetic molecular junctions

Abstract

Single molecule magnets and single spin centres can be individually addressed when coupled to contacts forming an electrical junction. To control and engineer the magnetism of quantum devices, it is necessary to quantify how the structural and chemical environment of the junction affects the spin centre. Metrics such as coordination number or symmetry provide a simple method to quantify the local environment, but neglect the many-body interactions of an impurity spin coupled to contacts. Here, we utilize a highly corrugated hexagonal boron nitride monolayer to mediate the coupling between a cobalt spin in CoHx (x=1,2) complexes and the metal contact. While hydrogen controls the total effective spin, the corrugation smoothly tunes the Kondo exchange interaction between the spin and the underlying metal. Using scanning tunnelling microscopy and spectroscopy together with numerical simulations, we quantitatively demonstrate how the Kondo exchange interaction mimics chemical tailoring and changes the magnetic anisotropy.

Competition between quantum spin tunneling and Kondo effect

“…Our calculations permit to trace the evolution from the weak Kondo coupling regime, where the stepwise dI/dV spectra are renormalized, resulting in the shift and the broadening of the spin excitation energies, to the strong coupling regime, where the zero bias Kondo peak appears. This accounts for several experimental observations [17,20]. For strong Kondo coupling, QST can be completely quenched.…”

“…We neglect direct tunneling into surface states in equation (1). This is a good approximation when the magnetic atoms are separated from the metallic surface by a decoupling insulating layer, such as Cu 2 N/Cu(100) [4,17,19], CuO/Cu [6] and h-BN/Rh(111) [20]. This approximation does not capture the Fano interference effect relevant [12] when the tipatom channel interferes with the direct tip-surface tunneling path [29].…”

“…Moreover, the joint observation of a zero bias Kondo resonance together with stepwise inelastic spin excitations has been reported for individual magnetic atoms [17,19]. Importantly, it is possible to devise experiments [8,17,20] in which the Kondo interaction could be tuned, making it relevant to address the question of how the G(V ) spectra evolve from the weak to the strong coupling regime. The magnitude of the quantum spin tunneling splitting can also be modulated by application of a magnetic field along the hard axis direction [13,14].…”

Electronic properties of transition metal atoms onCu2N/Cu(100)

“…Finally, we expect that our analysis should also be applicable to other systems with magnetic adatoms and molecules deposited in conducting surfaces whose spin excitations can be described in terms of quantized spin models [66,[69][70][71][72].…”

RKKY oscillations in the spin relaxation rates of atomic-scale nanomagnets

“…Application of this equation for a single anisotropic spin results in the renormalization of the single-spin anisotropy due to Kondo exchange [54,58] observed experimentally [27,58]. Equation (17) can be formally connected with the conventional RKKY formulas if we replace the matrix elements S a MR (n) with the a component of a classical magnetic moment at atom n, and we take the static limit where ω MR = 0.…”